The immediate goal of this research is to construct an effective, nontoxic acellular vaccine against infection by Bordetella pertussis. Pertussis toxin is an extracellular protein produced by B. Pertussis that is both a determinant of virulence and an antigen that elicits protective immunity. Conditions will be established to produce a toxoid of pertussis toxin that lacks cytotoxicity but retains immunogenicity. The genetically engineered toxoid of pertussis toxin will be tested alone and with other antigens of B. pertussis as acellular vaccine candidates. The long-term goals are to develop strategies for the construction of an acellular vaccine against B. pertussis that are applicable for the generation of recombinant DNA-derived acellular vaccines against other bacterial !pathogens. The research project described will define the catalytic properties of the Sl subunit of pertussis toxin. The aim is to define the function of specific residues within the Sl subunit that reduce toxicity but retain immunogenicity. This research will also focus on determining the mechanism of action of pertussis toxin by defining how pertussis toxin is activated, enters sensitive cells, and interacts with G-proteins.